WHAT IS A TIDAL FLAT?

Tidal flats are sand or mud areas found in many estuarine areas and typically lack recognizable plant life (Fig. 1).  They are neither terrestrial nor aquatic but fall somewhere in between (ecotone) and are harsh, unpredictable environments.  In the central and southern Texas coast, tidal flats replace salt marshes because there is little freshwater inflow to the estuaries from rivers or streams and there is little rain.  Tidal flats appear to be barren wastelands but they are, in fact, highly productive areas that support large numbers of animals, particularly shorebirds (Fig. 2).  The extent to which tidal flats contribute to the flow of energy within an estuary is mostly determined by how frequently they are flooded with seawater and the length of time they are exposed.

In the Coastal Bend of Texas, tidal flats are typically called “wind-tidal flats” because the wind, rather than astronomical tides, causes them to be flooded or exposed.  Because the wind is responsible for flooding or exposure, both occur at irregular intervals and the speed of either is determined by wind speed and direction.  Tidal flats in other areas, such as the Atlantic Coast, are flooded and exposed at more regular intervals (usually daily) and for longer periods of time because astronomical tides are mostly responsible.

Fig. 1.  View of a typical tidal flat.

Fig 2.  Shorebirds on the tidal flat.

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